1. Field
Embodiments of the present invention relate to apparatuses and methods for loading particulate materials into vertical tubes, more particularly apparatuses and methods for loading catalysts into columns of conversion furnaces of hydrogen generation units.
2. Description of Related Art
Oil refineries usually use a large volume of hydrogen in their processes. This hydrogen normally comes from hydrogen generation units, where conversion furnaces having dozens or, in some cases, hundreds of vertical columns filled with particles of catalyst are used to exchange heat. After a certain amount of operation time, the spent catalyst in the vertical tubes must be replaced. To replace the spent catalyst it is necessary to use methods and apparatuses to load particles of catalyst into the interior of the vertical tubes.
In these cases the loading must be carried out carefully to avoid problems caused by the presence of empty internal spaces and variations in density in the load of the catalyst. Other possible problems include breakage of or damage to the particles of catalyst during the loading. For example, when the particles are dropped from a great height, depending on the length of the vertical column, the impact with the walls, or even the bottom of the column, can cause the particles of catalyst to break or be damaged, harming the efficiency of the catalyst.
If there are broken particles, or there are too many empty spaces in the interior of the column loaded with solid particles, this results in variations in density of catalyst over the length of the column. As a consequence, the pressure of the operation in the column varies, which generates distortions in the distribution of the gas in the reactor of the conversion furnaces and causes unequal distributions of temperature over the length of the columns during the operation of the conversion furnace.
Usually, to reduce the empty spaces or to make the density of the catalyst uniform, a vertical column can be vibrated, over its length, or receive blows to its upper part during the loading of the particulate material. However, this operation normally delays the loading, and also submits the column to further tension, reducing its useful life or causing irreparable damage. If an excessive quantity of catalyst has been damaged during the loading, the only solution is usually to remove all the catalyst from the interior of the column and carry out a new loading, requiring duplication of the work and loss of catalyst.
In another loading method for particulate material used to reduce the variation of density of the material distributed in the vertical column of conversion furnaces, socks made of plastic material and filled with catalyst are used. When loading all the volume of material into the column, the sock is held by a thread and lowered to the bottom of each column. With a pull on the thread, the sock is opened and the catalyst is deposited in the interior of the column, traveling a small distance in free fall, which avoids breakage.
However, there are some disadvantages in using of this method. Sometimes the sock may open early, allowing the particles of catalyst to travel a larger distance in free fall, which can result in breakage or damage to the particles.
Further, if there are empty spaces between the particles in the interior of the sock, there will also be the same empty spaces within the vertical column at the completion of loading. Consequently, the vertical column must receive additional vibration or blows to make its density homogenous.
Another method of loading particulate material in vertical tubes is shown in patent number EP 1.594.605 B1. In this method, the particulate material is transported to the bottom of the tube by a damper made of a spiral rod. The rod in EP 1.594.605 B1 is continuous and extends for the whole of the length of the tube to be filled. As the particulate material is loaded, the rod is gradually lifted, being turned or vibrated during the loading from its upper limit. In this case, disadvantages are seen such as: causing damage to the tube due to the possible impact between the rod and the tube; the complexity of the operation, since the rod has to be lifted gradually; the need for a piece of equipment to make the rod turn or vibrate, which generates additional operation costs; and the difficulty of handling the rod, which has a length similar to that of the tube.
Exemplary embodiments of apparatuses and methods consistent with those described below may constitute an advantageous alternative for the loading of particulate material in a vertical tube, in relation to the methods discussed above.